In recent years, technology known as OpenFlow has been proposed (refer to Patent Literature 1, and Non-Patent Literature 1 and 2). In OpenFlow communication is taken as end-to-end flow, and path control, failure recovery, load balancing, and optimization are performed on a per-flow basis. An OpenFlow switch functioning as a relay device is provided with a secure channel for communication with an OpenFlow controller positioned as a control apparatus, and operates according to a flow table in which appropriate addition or rewriting is instructed by the OpenFlow controller. In the flow table, for each flow there are definitions of sets of matching rules (Header Fields) for collation with packet headers, flow statistical information (Counters), and Instructions that define processing content to be applied to packets matching a matching rule (Header Fields) (refer to “4.1 Flow Table” and following, in Non Patent Literature 2).
For example, when an OpenFlow switch receives a packet, a search is made for an entry that has a matching rule that matches header information of the received packet, from the flow table. As a result of the search, in a case where an entry matching the received packet is found, the OpenFlow switch updates the flow statistical information (Counters) and also implements processing content (packet transmission from a specified port, flooding, dropping, and the like) described in an Actions field of the entry in question, for the received packet. On the other hand, as a result of the search, in a case where an entry matching the received packet is not found, the OpenFlow switch forwards the received packet to the OpenFlow controller via a secure channel, requests determination of a path of the packet based on source and destination of the received packet, receives a flow entry realizing this, and updates the flow table. In this way, the OpenFlow switch uses the entry stored in the flow table as a processing rule to perform packet forwarding.
Patent Literature 2 discloses a method of analyzing content at a network entrance, attaching a label to a packet, and thereafter selecting a path by a label base.
[Patent Literature 1]
    PCT International Publication No. 2008/095010[Patent Literature 2]    Japanese Patent Kokai Publication No. JP2006-203904A[Non-Patent Literature 1]    Nick McKeown and seven other authors, “OpenFlow: Enabling Innovation in Campus Networks”, [online], [search conducted on Feb. 14, 2012], Internet: <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf>[Non-Patent Literature 2]    “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02) Feb. 14, 2012, [online], [search conducted on Feb. 14, 2012], Internet: <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf >